Clarify that "hidden" votes in closed polls and similar are not secret on a technical level

### Your use case

#### What would you like to do?
Polls currently have 2 features that imply a level of secrecy:
1. "Voters see results as soon as they have voted" - i.e. "secret" until you vote
2. On top of that closed polls "Results are only revealed when you end the poll" - i.e. "secret" until the poll creator reveals the results

In fact however, this apparent secrecy is based on client compliance (not) rendering the received events. It becomes especially apparent when I create a closed poll on develop, and another user on stable which at the time did not support closed polls was confused about what novelty I was showing off.

#### Why would you like to do it?
Manage user expectations.

This will be even more relevant across clients that are not kept in sync as closely as the stable element flavours.

#### How would you like to achieve it?

Clicking/hovering this `?` will show a tooltip that further explains the situation.

### Have you considered any alternatives?

_No response_

### Additional context

https://github.com/vector-im/element-web/issues/21176#issuecomment-1083368331

Review the existing closed-poll and vote-result wording, along with the proposed question-mark tooltip shown in the issue image. Confirm that the tooltip explains that hidden results are not technically secret across clients, and verify the wording for both listed poll behaviours. The issue names no files or tests, so locating the poll UI entry point is the first research step.

Written by the indexing model from the issue text.